pulseaudio: Respect pulseaudio env vars and config file
pulseaudio: Respect pulseaudio env vars and config file

Instead of just assuming the default pulseaudio socket we look
at the same environment and config files that pulseaudio does.

This does not currently look at the X11 properties.

This is a cleaned up and rebased version of https://github.com/flatpak/flatpak/pull/1208

Closes: #1410
Approved by: alexlarsson

flatpak/flatpak,flatpak/flatpak,handsome-feng/flatpak,flatpak/flatpak,matthiasclasen/flatpak,handsome-feng/flatpak,flatpak/flatpak,handsome-feng/flatpak,handsome-feng/flatpak,matthiasclasen/flatpak,flatpak/flatpak,matthiasclasen/flatpak,handsome-feng/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak